New safeguards on the arrest of terror suspects will be demanded this week by a high-powered Commons inquiry amid warnings that the police are making 'preventative' arrests of people who have not yet offended.

The move follows the raid on the home of two brothers, one of whom was shot, in Forest Gate, east London. Despite claims of a poison bomb plot, the Metropolitan Police were forced to apologise when nothing was found and both men were released without charge, prompting a bitter dispute between police and security services over the intelligence on which the raid was based.

In a report to be published days before the anniversary of the 7 July bombings, the home affairs select committee will argue that the police have become so afraid of failing to prevent another atrocity they are arresting people on suspicion they may attack in future, a situation not provided for in British law. It will call for security-vetted judges to approve in advance arrests made on the basis of intelligence rather than hard evidence.

'The evidence was that a lot of arrests take place early because you are trying to disrupt a conspiracy before anyone gets killed - preventative arrests essentially,' said a committee source.